The invention relates to a device and a method for producing organic amino compounds from organic nitro compounds, wherein the organic nitro compound is hydrogenated to the organic amino compound with a hydrogen-containing gas stream by means of a catalyst, the reaction course of the hydrogenation being monitored by analysis of secondary products forming during hydrogenation.
The production of organic amino compounds from corresponding nitro compounds is sufficiently known. In the method described in EP 0 223 035 A1 the hydrogenation is performed with the aid of modified Raney nickel catalysts dispersed in the liquid reaction mixture. The catalyst can be separated out of the liquid reaction mixture by filtration or sedimentation and optionally returned to the process.
Furthermore, a method for producing toluylene diamine by hydrogenation of dinitrotoluene at elevated temperature and elevated pressure at one reactor or at two reactors connected in series is known from DE 2044657. High-pressure tubular-flow reactors containing fixed nickel or ruthenium hydrogenating catalysts are proposed as reactors.
Organic amino compounds, in particular diamino or triamino compounds, are an important starting substance for the production of organic polyisocyanates, which in turn are needed for polyurethane production. To this end, toluylene diamine (TDA), for example, a commonly used monomer for polyisocyanate production, is produced via a hydrogenation starting from dinitrotoluene. Catalysts are typically used for the hydrogenation, which is performed in the liquid phase. During the course of the production process problems can arise, through insufficient catalyst activity for example, such that an accumulation of dinitrotoluene occurs in the reactor. This accumulation can present a considerable safety risk, since dinitrotoluene can decompose explosively at elevated temperature and in particular in the presence of strong bases. In order to mitigate this safety risk, complete reaction of the dinitrotoluene that is added to the hydrogenating reactor is desired. A number of approaches to this end are known.
WO 03/066571 A1 discloses the performance of the hydrogenation reaction to completion through analysis of the liquid hydrogenation product by gas chromatography.
DE 10 2005 008 613 A1 proposes determining the concentration of nitro and nitroso compounds by UV/VIS absorption spectroscopy methods.
WO 2012/076449 A1 describes a method for producing aromatic amines by hydrogenating nitro aromatics, wherein a chromatographic analysis of the reaction mixture is performed in order to determine the concentration of nitro and nitroso compounds in the reaction mixture.
Furthermore, experienced plant operators can also draw conclusions about the reaction course from the color of the hydrogenation product. In addition, it is known the completeness of the reaction can also be assessed by monitoring the temperature rise in a reaction chamber connected downstream of the actual reactor. An incomplete reaction can moreover also be detected from a deviation of the reaction stoichiometry, specifically by analysing the ratio between hydrogen and dinitrotoluene. These methods are described for example in WO 2011/086050 A2.
However, the measures that have hitherto been known for checking the completeness of the hydrogenation reactions are not satisfactory in every respect.
Thus, some of these methods require complex equipment, while others rely on the experience of the operating staff, which can inevitably lead to mistakes. Other methods, such as determining the temperature rise for example, deliver the required data with a time delay, which is likewise disadvantageous for optimum control of the hydrogenating reactor.
The object of the present invention was therefore to provide a device and a method for producing organic amines by the hydrogenation of corresponding nitro compounds, which method can be implemented with comparatively inexpensive equipment and delivers timely information about the completeness of the hydrogenation reaction. The device and the method should be safe to use and should above all allow a quantitative reaction of the organic nitro compound combined with an optimised yield of organic amino compound.